text: // Copyright (c) 2012 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // This header is designed to give you trace_event macros without specifying
  // how the events actually get collected and stored. If you need to expose trace
  // event to some other universe, you can copy-and-paste this file,
  // implement the TRACE_EVENT_API macros, and do any other necessary fixup for
  // the target platform. The end result is that multiple libraries can funnel
  // events through to a shared trace event collector.
  
  // Trace events are for tracking application performance and resource usage.
  // Macros are provided to track:
  //    Begin and end of function calls
  //    Counters
  //
  // Events are issued against categories. Whereas LOG's
  // categories are statically defined, TRACE categories are created
  // implicitly with a string. For example:
  //   TRACE_EVENT_INSTANT0("MY_SUBSYSTEM", "SomeImportantEvent")
  //
  // Events can be INSTANT, or can be pairs of BEGIN and END in the same scope:
  //   TRACE_EVENT_BEGIN0("MY_SUBSYSTEM", "SomethingCostly")
  //   doSomethingCostly()
  //   TRACE_EVENT_END0("MY_SUBSYSTEM", "SomethingCostly")
  // Note: our tools can't always determine the correct BEGIN/END pairs unless
  // these are used in the same scope. Use ASYNC_BEGIN/ASYNC_END macros if you
  // need them to be in separate scopes.
  //
  // A common use case is to trace entire function scopes. This
  // issues a trace BEGIN and END automatically:
  //   void doSomethingCostly() {
  //     TRACE_EVENT0("MY_SUBSYSTEM", "doSomethingCostly");
  //     ...
  //   }
  //
  // Additional parameters can be associated with an event:
  //   void doSomethingCostly2(int howMuch) {
  //     TRACE_EVENT1("MY_SUBSYSTEM", "doSomethingCostly",
  //         "howMuch", howMuch);
  //     ...
  //   }
  //
  // The trace system will automatically add to this information the
  // current process id, thread id, and a timestamp in microseconds.
  //
  // To trace an asynchronous procedure such as an IPC send/receive, use
  // ASYNC_BEGIN and ASYNC_END:
  //   [single threaded sender code]
  //     static int send_count = 0;
  //     ++send_count;
  //     TRACE_EVENT_ASYNC_BEGIN0("ipc", "message", send_count);
  //     Send(new MyMessage(send_count));
  //   [receive code]
  //     void OnMyMessage(send_count) {
  //       TRACE_EVENT_ASYNC_END0("ipc", "message", send_count);
  //     }
  // The third parameter is a unique ID to match ASYNC_BEGIN/ASYNC_END pairs.
  // ASYNC_BEGIN and ASYNC_END can occur on any thread of any traced process.
  // Pointers can be used for the ID parameter, and they will be mangled
  // internally so that the same pointer on two different processes will not
  // match. For example:
  //   class MyTracedClass {
  //    public:
  //     MyTracedClass() {
  //       TRACE_EVENT_ASYNC_BEGIN0("category", "MyTracedClass", this);
  //     }
  //     ~MyTracedClass() {
  //       TRACE_EVENT_ASYNC_END0("category", "MyTracedClass", this);
  //     }
  //   }
  //
  // Trace event also supports counters, which is a way to track a quantity
  // as it varies over time. Counters are created with the following macro:
  //   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter", g_myCounterValue);
  //
  // Counters are process-specific. The macro itself can be issued from any
  // thread, however.
  //
  // Sometimes, you want to track two counters at once. You can do this with two
  // counter macros:
  //   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter0", g_myCounterValue[0]);
  //   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter1", g_myCounterValue[1]);
  // Or you can do it with a combined macro:
  //   TRACE_COUNTER2("MY_SUBSYSTEM", "myCounter",
  //       "bytesPinned", g_myCounterValue[0],
  //       "bytesAllocated", g_myCounterValue[1]);
  // This indicates to the tracing UI that these counters should be displayed
  // in a single graph, as a summed area chart.
  //
  // Since counters are in a global namespace, you may want to disembiguate with a
  // unique ID, by using the TRACE_COUNTER_ID* variations.
  //
  // By default, trace collection is compiled in, but turned off at runtime.
  // Collecting trace data is the responsibility of the embedding
  // application. In Chrome's case, navigating to about:tracing will turn on
  // tracing and display data collected across all active processes.
  //
  //
  // Memory scoping note:
  // Tracing copies the pointers, not the string content, of the strings passed
  // in for category, name, and arg_names.  Thus, the following code will
  // cause problems:
  //     char* str = strdup("impprtantName");
  //     TRACE_EVENT_INSTANT0("SUBSYSTEM", str);  // BAD!
  //     free(str);                   // Trace system now has dangling pointer
  //
  // To avoid this issue with the |name| and |arg_name| parameters, use the
  // TRACE_EVENT_COPY_XXX overloads of the macros at additional runtime overhead.
  // Notes: The category must always be in a long-lived char* (i.e. static const).
  //        The |arg_values|, when used, are always deep copied with the _COPY
  //        macros.
  //
  // When are string argument values copied:
  // const char* arg_values are only referenced by default:
  //     TRACE_EVENT1("category", "name",
  //                  "arg1", "literal string is only referenced");
  // Use TRACE_STR_COPY to force copying of a const char*:
  //     TRACE_EVENT1("category", "name",
  //                  "arg1", TRACE_STR_COPY("string will be copied"));
  // std::string arg_values are always copied:
  //     TRACE_EVENT1("category", "name",
  //                  "arg1", std::string("string will be copied"));
  //
  //
  // Thread Safety:
  // A thread safe singleton and mutex are used for thread safety. Category
  // enabled flags are used to limit the performance impact when the system
  // is not enabled.
  //
  // TRACE_EVENT macros first cache a pointer to a category. The categories are
  // statically allocated and safe at all times, even after exit. Fetching a
  // category is protected by the TraceLog::lock_. Multiple threads initializing
  // the static variable is safe, as they will be serialized by the lock and
  // multiple calls will return the same pointer to the category.
  //
  // Then the category_enabled flag is checked. This is a unsigned char, and
  // not intended to be multithread safe. It optimizes access to AddTraceEvent
  // which is threadsafe internally via TraceLog::lock_. The enabled flag may
  // cause some threads to incorrectly call or skip calling AddTraceEvent near
  // the time of the system being enabled or disabled. This is acceptable as
  // we tolerate some data loss while the system is being enabled/disabled and
  // because AddTraceEvent is threadsafe internally and checks the enabled state
  // again under lock.
  //
  // Without the use of these static category pointers and enabled flags all
  // trace points would carry a significant performance cost of aquiring a lock
  // and resolving the category.
  
  
  #ifndef BASE_DEBUG_TRACE_EVENT_H_
  #define BASE_DEBUG_TRACE_EVENT_H_
  
  #include <string>
  
  #include "base/atomicops.h"
  #include "base/debug/trace_event_impl.h"
  #include "build/build_config.h"
  
  // By default, const char* argument values are assumed to have long-lived scope
  // and will not be copied. Use this macro to force a const char* to be copied.
  #define TRACE_STR_COPY(str) \
      trace_event_internal::TraceStringWithCopy(str)
  
  // Records a pair of begin and end events called "name" for the current
  // scope, with 0, 1 or 2 associated arguments. If the category is not
  // enabled, then this does nothing.
  // - category and name strings must have application lifetime (statics or
  //   literals). They may not include " chars.
  #define TRACE_EVENT0(category, name) \
      INTERNAL_TRACE_EVENT_ADD_SCOPED(category, name)
  #define TRACE_EVENT1(category, name, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD_SCOPED(category, name, arg1_name, arg1_val)
  #define TRACE_EVENT2(category, name, arg1_name, arg1_val, arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD_SCOPED(category, name, arg1_name, arg1_val, \
          arg2_name, arg2_val)
  
  // Same as TRACE_EVENT except that they are not included in official builds.
  #ifdef OFFICIAL_BUILD
  #define UNSHIPPED_TRACE_EVENT0(category, name) (void)0
  #define UNSHIPPED_TRACE_EVENT1(category, name, arg1_name, arg1_val) (void)0
  #define UNSHIPPED_TRACE_EVENT2(category, name, arg1_name, arg1_val, \
                                 arg2_name, arg2_val) (void)0
  #define UNSHIPPED_TRACE_EVENT_INSTANT0(category, name) (void)0
  #define UNSHIPPED_TRACE_EVENT_INSTANT1(category, name, arg1_name, arg1_val) \
      (void)0
  #define UNSHIPPED_TRACE_EVENT_INSTANT2(category, name, arg1_name, arg1_val, \
                                         arg2_name, arg2_val) (void)0
  #else
  #define UNSHIPPED_TRACE_EVENT0(category, name) \
      TRACE_EVENT0(category, name)
  #define UNSHIPPED_TRACE_EVENT1(category, name, arg1_name, arg1_val) \
      TRACE_EVENT1(category, name, arg1_name, arg1_val)
  #define UNSHIPPED_TRACE_EVENT2(category, name, arg1_name, arg1_val, \
                                 arg2_name, arg2_val) \
      TRACE_EVENT2(category, name, arg1_name, arg1_val, arg2_name, arg2_val)
  #define UNSHIPPED_TRACE_EVENT_INSTANT0(category, name) \
      TRACE_EVENT_INSTANT0(category, name)
  #define UNSHIPPED_TRACE_EVENT_INSTANT1(category, name, arg1_name, arg1_val) \
      TRACE_EVENT_INSTANT1(category, name, arg1_name, arg1_val)
  #define UNSHIPPED_TRACE_EVENT_INSTANT2(category, name, arg1_name, arg1_val, \
                                         arg2_name, arg2_val) \
      TRACE_EVENT_INSTANT2(category, name, arg1_name, arg1_val, \
                           arg2_name, arg2_val)
  #endif
  
  // Records a single event called "name" immediately, with 0, 1 or 2
  // associated arguments. If the category is not enabled, then this
  // does nothing.
  // - category and name strings must have application lifetime (statics or
  //   literals). They may not include " chars.
  #define TRACE_EVENT_INSTANT0(category, name) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
          category, name, TRACE_EVENT_FLAG_NONE)
  #define TRACE_EVENT_INSTANT1(category, name, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
          category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
  #define TRACE_EVENT_INSTANT2(category, name, arg1_name, arg1_val, \
          arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
          category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, \
          arg2_name, arg2_val)
  #define TRACE_EVENT_COPY_INSTANT0(category, name) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
          category, name, TRACE_EVENT_FLAG_COPY)
  #define TRACE_EVENT_COPY_INSTANT1(category, name, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
          category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
  #define TRACE_EVENT_COPY_INSTANT2(category, name, arg1_name, arg1_val, \
          arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
          category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, \
          arg2_name, arg2_val)
  
  // Records a single BEGIN event called "name" immediately, with 0, 1 or 2
  // associated arguments. If the category is not enabled, then this
  // does nothing.
  // - category and name strings must have application lifetime (statics or
  //   literals). They may not include " chars.
  #define TRACE_EVENT_BEGIN0(category, name) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
          category, name, TRACE_EVENT_FLAG_NONE)
  #define TRACE_EVENT_BEGIN1(category, name, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
          category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
  #define TRACE_EVENT_BEGIN2(category, name, arg1_name, arg1_val, \
          arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
          category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, \
          arg2_name, arg2_val)
  #define TRACE_EVENT_COPY_BEGIN0(category, name) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
          category, name, TRACE_EVENT_FLAG_COPY)
  #define TRACE_EVENT_COPY_BEGIN1(category, name, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
          category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
  #define TRACE_EVENT_COPY_BEGIN2(category, name, arg1_name, arg1_val, \
          arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
          category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, \
          arg2_name, arg2_val)
  
  // Records a single END event for "name" immediately. If the category
  // is not enabled, then this does nothing.
  // - category and name strings must have application lifetime (statics or
  //   literals). They may not include " chars.
  #define TRACE_EVENT_END0(category, name) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
          category, name, TRACE_EVENT_FLAG_NONE)
  #define TRACE_EVENT_END1(category, name, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
          category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
  #define TRACE_EVENT_END2(category, name, arg1_name, arg1_val, \
          arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
          category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, \
          arg2_name, arg2_val)
  #define TRACE_EVENT_COPY_END0(category, name) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
          category, name, TRACE_EVENT_FLAG_COPY)
  #define TRACE_EVENT_COPY_END1(category, name, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
          category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
  #define TRACE_EVENT_COPY_END2(category, name, arg1_name, arg1_val, \
          arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
          category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, \
          arg2_name, arg2_val)
  
  // Time threshold event:
  // Only record the event if the duration is greater than the specified
  // threshold_us (time in microseconds).
  // Records a pair of begin and end events called "name" for the current
  // scope, with 0, 1 or 2 associated arguments. If the category is not
  // enabled, then this does nothing.
  // - category and name strings must have application lifetime (statics or
  //   literals). They may not include " chars.
  #define TRACE_EVENT_IF_LONGER_THAN0(threshold_us, category, name) \
      INTERNAL_TRACE_EVENT_ADD_SCOPED_IF_LONGER_THAN(threshold_us, category, name)
  #define TRACE_EVENT_IF_LONGER_THAN1( \
      threshold_us, category, name, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD_SCOPED_IF_LONGER_THAN( \
          threshold_us, category, name, arg1_name, arg1_val)
  #define TRACE_EVENT_IF_LONGER_THAN2( \
      threshold_us, category, name, arg1_name, arg1_val, arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD_SCOPED_IF_LONGER_THAN( \
          threshold_us, category, name, arg1_name, arg1_val, arg2_name, arg2_val)
  
  // Records the value of a counter called "name" immediately. Value
  // must be representable as a 32 bit integer.
  // - category and name strings must have application lifetime (statics or
  //   literals). They may not include " chars.
  #define TRACE_COUNTER1(category, name, value) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, \
          category, name, TRACE_EVENT_FLAG_NONE, \
          "value", static_cast<int>(value))
  #define TRACE_COPY_COUNTER1(category, name, value) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, \
          category, name, TRACE_EVENT_FLAG_COPY, \
          "value", static_cast<int>(value))
  
  // Records the values of a multi-parted counter called "name" immediately.
  // The UI will treat value1 and value2 as parts of a whole, displaying their
  // values as a stacked-bar chart.
  // - category and name strings must have application lifetime (statics or
  //   literals). They may not include " chars.
  #define TRACE_COUNTER2(category, name, value1_name, value1_val, \
          value2_name, value2_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, \
          category, name, TRACE_EVENT_FLAG_NONE, \
          value1_name, static_cast<int>(value1_val), \
          value2_name, static_cast<int>(value2_val))
  #define TRACE_COPY_COUNTER2(category, name, value1_name, value1_val, \
          value2_name, value2_val) \
      INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, \
          category, name, TRACE_EVENT_FLAG_COPY, \
          value1_name, static_cast<int>(value1_val), \
          value2_name, static_cast<int>(value2_val))
  
  // Records the value of a counter called "name" immediately. Value
  // must be representable as a 32 bit integer.
  // - category and name strings must have application lifetime (statics or
  //   literals). They may not include " chars.
  // - |id| is used to disambiguate counters with the same name. It must either
  //   be a pointer or an integer value up to 64 bits. If it's a pointer, the bits
  //   will be xored with a hash of the process ID so that the same pointer on
  //   two different processes will not collide.
  #define TRACE_COUNTER_ID1(category, name, id, value) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, \
          category, name, id, TRACE_EVENT_FLAG_NONE, \
          "value", static_cast<int>(value))
  #define TRACE_COPY_COUNTER_ID1(category, name, id, value) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, \
          category, name, id, TRACE_EVENT_FLAG_COPY, \
          "value", static_cast<int>(value))
  
  // Records the values of a multi-parted counter called "name" immediately.
  // The UI will treat value1 and value2 as parts of a whole, displaying their
  // values as a stacked-bar chart.
  // - category and name strings must have application lifetime (statics or
  //   literals). They may not include " chars.
  // - |id| is used to disambiguate counters with the same name. It must either
  //   be a pointer or an integer value up to 64 bits. If it's a pointer, the bits
  //   will be xored with a hash of the process ID so that the same pointer on
  //   two different processes will not collide.
  #define TRACE_COUNTER_ID2(category, name, id, value1_name, value1_val, \
          value2_name, value2_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, \
          category, name, id, TRACE_EVENT_FLAG_NONE, \
          value1_name, static_cast<int>(value1_val), \
          value2_name, static_cast<int>(value2_val))
  #define TRACE_COPY_COUNTER_ID2(category, name, id, value1_name, value1_val, \
          value2_name, value2_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, \
          category, name, id, TRACE_EVENT_FLAG_COPY, \
          value1_name, static_cast<int>(value1_val), \
          value2_name, static_cast<int>(value2_val))
  
  
  // Records a single ASYNC_BEGIN event called "name" immediately, with 0, 1 or 2
  // associated arguments. If the category is not enabled, then this
  // does nothing.
  // - category and name strings must have application lifetime (statics or
  //   literals). They may not include " chars.
  // - |id| is used to match the ASYNC_BEGIN event with the ASYNC_END event. ASYNC
  //   events are considered to match if their category, name and id values all
  //   match. |id| must either be a pointer or an integer value up to 64 bits. If
  //   it's a pointer, the bits will be xored with a hash of the process ID so
  //   that the same pointer on two different processes will not collide.
  // An asynchronous operation can consist of multiple phases. The first phase is
  // defined by the ASYNC_BEGIN calls. Additional phases can be defined using the
  // ASYNC_STEP_BEGIN macros. When the operation completes, call ASYNC_END.
  // An async operation can span threads and processes, but all events in that
  // operation must use the same |name| and |id|. Each event can have its own
  // args.
  #define TRACE_EVENT_ASYNC_BEGIN0(category, name, id) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
          category, name, id, TRACE_EVENT_FLAG_NONE)
  #define TRACE_EVENT_ASYNC_BEGIN1(category, name, id, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
          category, name, id, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
  #define TRACE_EVENT_ASYNC_BEGIN2(category, name, id, arg1_name, arg1_val, \
          arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
          category, name, id, TRACE_EVENT_FLAG_NONE, \
          arg1_name, arg1_val, arg2_name, arg2_val)
  #define TRACE_EVENT_COPY_ASYNC_BEGIN0(category, name, id) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
          category, name, id, TRACE_EVENT_FLAG_COPY)
  #define TRACE_EVENT_COPY_ASYNC_BEGIN1(category, name, id, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
          category, name, id, TRACE_EVENT_FLAG_COPY, \
          arg1_name, arg1_val)
  #define TRACE_EVENT_COPY_ASYNC_BEGIN2(category, name, id, arg1_name, arg1_val, \
          arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
          category, name, id, TRACE_EVENT_FLAG_COPY, \
          arg1_name, arg1_val, arg2_name, arg2_val)
  
  // Records a single ASYNC_STEP event for |step| immediately. If the category
  // is not enabled, then this does nothing. The |name| and |id| must match the
  // ASYNC_BEGIN event above. The |step| param identifies this step within the
  // async event. This should be called at the beginning of the next phase of an
  // asynchronous operation.
  #define TRACE_EVENT_ASYNC_BEGIN_STEP0(category, name, id, step) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP, \
          category, name, id, TRACE_EVENT_FLAG_NONE, "step", step)
  #define TRACE_EVENT_ASYNC_BEGIN_STEP1(category, name, id, step, \
                                        arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP, \
          category, name, id, TRACE_EVENT_FLAG_NONE, "step", step, \
          arg1_name, arg1_val)
  #define TRACE_EVENT_COPY_ASYNC_BEGIN_STEP0(category, name, id, step) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP, \
          category, name, id, TRACE_EVENT_FLAG_COPY, "step", step)
  #define TRACE_EVENT_COPY_ASYNC_BEGIN_STEP1(category, name, id, step, \
          arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP, \
          category, name, id, TRACE_EVENT_FLAG_COPY, "step", step, \
          arg1_name, arg1_val)
  
  // Records a single ASYNC_END event for "name" immediately. If the category
  // is not enabled, then this does nothing.
  #define TRACE_EVENT_ASYNC_END0(category, name, id) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
          category, name, id, TRACE_EVENT_FLAG_NONE)
  #define TRACE_EVENT_ASYNC_END1(category, name, id, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
          category, name, id, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
  #define TRACE_EVENT_ASYNC_END2(category, name, id, arg1_name, arg1_val, \
          arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
          category, name, id, TRACE_EVENT_FLAG_NONE, \
          arg1_name, arg1_val, arg2_name, arg2_val)
  #define TRACE_EVENT_COPY_ASYNC_END0(category, name, id) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
          category, name, id, TRACE_EVENT_FLAG_COPY)
  #define TRACE_EVENT_COPY_ASYNC_END1(category, name, id, arg1_name, arg1_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
          category, name, id, TRACE_EVENT_FLAG_COPY, \
          arg1_name, arg1_val)
  #define TRACE_EVENT_COPY_ASYNC_END2(category, name, id, arg1_name, arg1_val, \
          arg2_name, arg2_val) \
      INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
          category, name, id, TRACE_EVENT_FLAG_COPY, \
          arg1_name, arg1_val, arg2_name, arg2_val)
  
  
  ////////////////////////////////////////////////////////////////////////////////
  // Implementation specific tracing API definitions.
  
  // Get a pointer to the enabled state of the given trace category. Only
  // long-lived literal strings should be given as the category name. The returned
  // pointer can be held permanently in a local static for example. If the
  // unsigned char is non-zero, tracing is enabled. If tracing is enabled,
  // TRACE_EVENT_API_ADD_TRACE_EVENT can be called. It's OK if tracing is disabled
  // between the load of the tracing state and the call to
  // TRACE_EVENT_API_ADD_TRACE_EVENT, because this flag only provides an early out
  // for best performance when tracing is disabled.
  // const unsigned char*
  //     TRACE_EVENT_API_GET_CATEGORY_ENABLED(const char* category_name)
  #define TRACE_EVENT_API_GET_CATEGORY_ENABLED \
      base::debug::TraceLog::GetCategoryEnabled
  
  // Add a trace event to the platform tracing system. Returns thresholdBeginId
  // for use in a corresponding end TRACE_EVENT_API_ADD_TRACE_EVENT call.
  // int TRACE_EVENT_API_ADD_TRACE_EVENT(
  //                    char phase,
  //                    const unsigned char* category_enabled,
  //                    const char* name,
  //                    unsigned long long id,
  //                    int num_args,
  //                    const char** arg_names,
  //                    const unsigned char* arg_types,
  //                    const unsigned long long* arg_values,
  //                    int threshold_begin_id,
  //                    long long threshold,
  //                    unsigned char flags)
  #define TRACE_EVENT_API_ADD_TRACE_EVENT \
      base::debug::TraceLog::GetInstance()->AddTraceEvent
  
  ////////////////////////////////////////////////////////////////////////////////
  
  // Implementation detail: trace event macros create temporary variables
  // to keep instrumentation overhead low. These macros give each temporary
  // variable a unique name based on the line number to prevent name collissions.
  #define INTERNAL_TRACE_EVENT_UID3(a,b) \
      trace_event_unique_##a##b
  #define INTERNAL_TRACE_EVENT_UID2(a,b) \
      INTERNAL_TRACE_EVENT_UID3(a,b)
  #define INTERNAL_TRACE_EVENT_UID(name_prefix) \
      INTERNAL_TRACE_EVENT_UID2(name_prefix, __LINE__)
  
  // Implementation detail: internal macro to create static category.
  // No barriers are needed, because this code is designed to operate safely
  // even when the unsigned char* points to garbage data (which may be the case
  // on processors without cache coherency).
  #define INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category) \
      static base::subtle::AtomicWord INTERNAL_TRACE_EVENT_UID(atomic) = 0; \
      const uint8* INTERNAL_TRACE_EVENT_UID(catstatic) = \
          reinterpret_cast<const uint8*>( \
              base::subtle::NoBarrier_Load(&INTERNAL_TRACE_EVENT_UID(atomic))); \
      if (!INTERNAL_TRACE_EVENT_UID(catstatic)) { \
        INTERNAL_TRACE_EVENT_UID(catstatic) = \
            TRACE_EVENT_API_GET_CATEGORY_ENABLED(category); \
        base::subtle::NoBarrier_Store(&INTERNAL_TRACE_EVENT_UID(atomic), \
            reinterpret_cast<base::subtle::AtomicWord>( \
                INTERNAL_TRACE_EVENT_UID(catstatic))); \
      }
  
  // Implementation detail: internal macro to create static category and add
  // event if the category is enabled.
  #define INTERNAL_TRACE_EVENT_ADD(phase, category, name, flags, ...) \
      do { \
        INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category); \
        if (*INTERNAL_TRACE_EVENT_UID(catstatic)) { \
          trace_event_internal::AddTraceEvent( \
              phase, INTERNAL_TRACE_EVENT_UID(catstatic), name, \
              trace_event_internal::kNoEventId, flags, ##__VA_ARGS__); \
        } \
      } while (0)
  
  // Implementation detail: internal macro to create static category and add begin
  // event if the category is enabled. Also adds the end event when the scope
  // ends.
  #define INTERNAL_TRACE_EVENT_ADD_SCOPED(category, name, ...) \
      INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category); \
      trace_event_internal::TraceEndOnScopeClose \
          INTERNAL_TRACE_EVENT_UID(profileScope); \
      if (*INTERNAL_TRACE_EVENT_UID(catstatic)) { \
        trace_event_internal::AddTraceEvent( \
            TRACE_EVENT_PHASE_BEGIN, \
            INTERNAL_TRACE_EVENT_UID(catstatic), \
            name, trace_event_internal::kNoEventId, \
            TRACE_EVENT_FLAG_NONE, ##__VA_ARGS__); \
        INTERNAL_TRACE_EVENT_UID(profileScope).Initialize( \
            INTERNAL_TRACE_EVENT_UID(catstatic), name); \
      }
  
  // Implementation detail: internal macro to create static category and add begin
  // event if the category is enabled. Also adds the end event when the scope
  // ends. If the elapsed time is < threshold time, the begin/end pair is erased.
  #define INTERNAL_TRACE_EVENT_ADD_SCOPED_IF_LONGER_THAN(threshold, \
          category, name, ...) \
      INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category); \
      trace_event_internal::TraceEndOnScopeCloseThreshold \
          INTERNAL_TRACE_EVENT_UID(profileScope); \
      if (*INTERNAL_TRACE_EVENT_UID(catstatic)) { \
        int INTERNAL_TRACE_EVENT_UID(begin_event_id) = \
          trace_event_internal::AddTraceEvent( \
              TRACE_EVENT_PHASE_BEGIN, \
              INTERNAL_TRACE_EVENT_UID(catstatic), \
              name, trace_event_internal::kNoEventId, \
              TRACE_EVENT_FLAG_NONE, ##__VA_ARGS__); \
        INTERNAL_TRACE_EVENT_UID(profileScope).Initialize( \
            INTERNAL_TRACE_EVENT_UID(catstatic), name, \
            INTERNAL_TRACE_EVENT_UID(begin_event_id), threshold); \
      }
  
  // Implementation detail: internal macro to create static category and add
  // event if the category is enabled.
  #define INTERNAL_TRACE_EVENT_ADD_WITH_ID(phase, category, name, id, flags, \
                                           ...) \
      do { \
        INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category); \
        if (*INTERNAL_TRACE_EVENT_UID(catstatic)) { \
          unsigned char trace_event_flags = flags | TRACE_EVENT_FLAG_HAS_ID; \
          trace_event_internal::TraceID trace_event_trace_id( \
              id, &trace_event_flags); \
          trace_event_internal::AddTraceEvent( \
              phase, INTERNAL_TRACE_EVENT_UID(catstatic), \
              name, trace_event_trace_id.data(), trace_event_flags, \
              ##__VA_ARGS__); \
        } \
      } while (0)
  
  // Notes regarding the following definitions:
  // New values can be added and propagated to third party libraries, but existing
  // definitions must never be changed, because third party libraries may use old
  // definitions.
  
  // Phase indicates the nature of an event entry. E.g. part of a begin/end pair.
  #define TRACE_EVENT_PHASE_BEGIN    ('B')
  #define TRACE_EVENT_PHASE_END      ('E')
  #define TRACE_EVENT_PHASE_INSTANT  ('I')
  #define TRACE_EVENT_PHASE_ASYNC_BEGIN ('S')
  #define TRACE_EVENT_PHASE_ASYNC_STEP  ('T')
  #define TRACE_EVENT_PHASE_ASYNC_END   ('F')
  #define TRACE_EVENT_PHASE_METADATA ('M')
  #define TRACE_EVENT_PHASE_COUNTER  ('C')
  
  // Flags for changing the behavior of TRACE_EVENT_API_ADD_TRACE_EVENT.
  #define TRACE_EVENT_FLAG_NONE        (static_cast<unsigned char>(0))
  #define TRACE_EVENT_FLAG_COPY        (static_cast<unsigned char>(1 << 0))
  #define TRACE_EVENT_FLAG_HAS_ID      (static_cast<unsigned char>(1 << 1))
  #define TRACE_EVENT_FLAG_MANGLE_ID   (static_cast<unsigned char>(1 << 2))
  
  // Type values for identifying types in the TraceValue union.
  #define TRACE_VALUE_TYPE_BOOL         (static_cast<unsigned char>(1))
  #define TRACE_VALUE_TYPE_UINT         (static_cast<unsigned char>(2))
  #define TRACE_VALUE_TYPE_INT          (static_cast<unsigned char>(3))
  #define TRACE_VALUE_TYPE_DOUBLE       (static_cast<unsigned char>(4))
  #define TRACE_VALUE_TYPE_POINTER      (static_cast<unsigned char>(5))
  #define TRACE_VALUE_TYPE_STRING       (static_cast<unsigned char>(6))
  #define TRACE_VALUE_TYPE_COPY_STRING  (static_cast<unsigned char>(7))
  
  namespace trace_event_internal {
  
  // Specify these values when the corresponding argument of AddTraceEvent is not
  // used.
  const int kZeroNumArgs = 0;
  const int kNoThreshholdBeginId = -1;
  const long long kNoThresholdValue = 0;
  const unsigned long long kNoEventId = 0;
  
  // TraceID encapsulates an ID that can either be an integer or pointer. Pointers
  // are mangled with the Process ID so that they are unlikely to collide when the
  // same pointer is used on different processes.
  class TraceID {
   public:
    explicit TraceID(const void* id, unsigned char* flags) :
        data_(static_cast<unsigned long long>(
            reinterpret_cast<unsigned long>(id))) {
      *flags |= TRACE_EVENT_FLAG_MANGLE_ID;
    }
    explicit TraceID(unsigned long long id, unsigned char* flags) :
        data_(id) { (void)flags; }
    explicit TraceID(unsigned long id, unsigned char* flags) :
        data_(id) { (void)flags; }
    explicit TraceID(unsigned int id, unsigned char* flags) :
        data_(id) { (void)flags; }
    explicit TraceID(unsigned short id, unsigned char* flags) :
        data_(id) { (void)flags; }
    explicit TraceID(unsigned char id, unsigned char* flags) :
        data_(id) { (void)flags; }
    explicit TraceID(long long id, unsigned char* flags) :
        data_(static_cast<unsigned long long>(id)) { (void)flags; }
    explicit TraceID(long id, unsigned char* flags) :
        data_(static_cast<unsigned long long>(id)) { (void)flags; }
    explicit TraceID(int id, unsigned char* flags) :
        data_(static_cast<unsigned long long>(id)) { (void)flags; }
    explicit TraceID(short id, unsigned char* flags) :
        data_(static_cast<unsigned long long>(id)) { (void)flags; }
    explicit TraceID(signed char id, unsigned char* flags) :
        data_(static_cast<unsigned long long>(id)) { (void)flags; }
  
    unsigned long long data() const { return data_; }
  
   private:
    unsigned long long data_;
  };
  
  // Simple union to store various types as unsigned long long.
  union TraceValueUnion {
    bool as_bool;
    unsigned long long as_uint;
    long long as_int;
    double as_double;
    const void* as_pointer;
    const char* as_string;
  };
  
  // Simple container for const char* that should be copied instead of retained.
  class TraceStringWithCopy {
   public:
    explicit TraceStringWithCopy(const char* str) : str_(str) {}
    operator const char* () const { return str_; }
   private:
    const char* str_;
  };
  
  // Define SetTraceValue for each allowed type. It stores the type and
  // value in the return arguments. This allows this API to avoid declaring any
  // structures so that it is portable to third_party libraries.
  #define INTERNAL_DECLARE_SET_TRACE_VALUE(actual_type, \
                                           union_member, \
                                           value_type_id) \
      static inline void SetTraceValue(actual_type arg, \
                                       unsigned char* type, \
                                       unsigned long long* value) { \
        TraceValueUnion type_value; \
        type_value.union_member = arg; \
        *type = value_type_id; \
        *value = type_value.as_uint; \
      }
  // Simpler form for int types that can be safely casted.
  #define INTERNAL_DECLARE_SET_TRACE_VALUE_INT(actual_type, \
                                               value_type_id) \
      static inline void SetTraceValue(actual_type arg, \
                                       unsigned char* type, \
                                       unsigned long long* value) { \
        *type = value_type_id; \
        *value = static_cast<unsigned long long>(arg); \
      }
  
  INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned long long, TRACE_VALUE_TYPE_UINT)
  INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned int, TRACE_VALUE_TYPE_UINT)
  INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned short, TRACE_VALUE_TYPE_UINT)
  INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned char, TRACE_VALUE_TYPE_UINT)
  INTERNAL_DECLARE_SET_TRACE_VALUE_INT(long long, TRACE_VALUE_TYPE_INT)
  INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int, TRACE_VALUE_TYPE_INT)
  INTERNAL_DECLARE_SET_TRACE_VALUE_INT(short, TRACE_VALUE_TYPE_INT)
  INTERNAL_DECLARE_SET_TRACE_VALUE_INT(signed char, TRACE_VALUE_TYPE_INT)
  INTERNAL_DECLARE_SET_TRACE_VALUE(bool, as_bool, TRACE_VALUE_TYPE_BOOL)
  INTERNAL_DECLARE_SET_TRACE_VALUE(double, as_double, TRACE_VALUE_TYPE_DOUBLE)
  INTERNAL_DECLARE_SET_TRACE_VALUE(const void*, as_pointer,
                                   TRACE_VALUE_TYPE_POINTER)
  INTERNAL_DECLARE_SET_TRACE_VALUE(const char*, as_string,
                                   TRACE_VALUE_TYPE_STRING)
  INTERNAL_DECLARE_SET_TRACE_VALUE(const TraceStringWithCopy&, as_string,
                                   TRACE_VALUE_TYPE_COPY_STRING)
  
  #undef INTERNAL_DECLARE_SET_TRACE_VALUE
  #undef INTERNAL_DECLARE_SET_TRACE_VALUE_INT
  
  // std::string version of SetTraceValue so that trace arguments can be strings.
  static inline void SetTraceValue(const std::string& arg,
                                   unsigned char* type,
                                   unsigned long long* value) {
    TraceValueUnion type_value;
    type_value.as_string = arg.c_str();
    *type = TRACE_VALUE_TYPE_COPY_STRING;
    *value = type_value.as_uint;
  }
  
  // These AddTraceEvent template functions are defined here instead of in the
  // macro, because the arg_values could be temporary objects, such as
  // std::string. In order to store pointers to the internal c_str and pass
  // through to the tracing API, the arg_values must live throughout
  // these procedures.
  
  static inline int AddTraceEvent(char phase,
                                  const unsigned char* category_enabled,
                                  const char* name,
                                  unsigned long long id,
                                  unsigned char flags) {
    return TRACE_EVENT_API_ADD_TRACE_EVENT(
        phase, category_enabled, name, id,
        kZeroNumArgs, NULL, NULL, NULL,
        kNoThreshholdBeginId, kNoThresholdValue, flags);
  }
  
  template<class ARG1_TYPE>
  static inline int AddTraceEvent(char phase,
                                  const unsigned char* category_enabled,
                                  const char* name,
                                  unsigned long long id,
                                  unsigned char flags,
                                  const char* arg1_name,
                                  const ARG1_TYPE& arg1_val) {
    const int num_args = 1;
    unsigned char arg_types[1];
    unsigned long long arg_values[1];
    SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
    return TRACE_EVENT_API_ADD_TRACE_EVENT(
        phase, category_enabled, name, id,
        num_args, &arg1_name, arg_types, arg_values,
        kNoThreshholdBeginId, kNoThresholdValue, flags);
  }
  
  template<class ARG1_TYPE, class ARG2_TYPE>
  static inline int AddTraceEvent(char phase,
                                  const unsigned char* category_enabled,
                                  const char* name,
                                  unsigned long long id,
                                  unsigned char flags,
                                  const char* arg1_name,
                                  const ARG1_TYPE& arg1_val,
                                  const char* arg2_name,
                                  const ARG2_TYPE& arg2_val) {
    const int num_args = 2;
    const char* arg_names[2] = { arg1_name, arg2_name };
    unsigned char arg_types[2];
    unsigned long long arg_values[2];
    SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
    SetTraceValue(arg2_val, &arg_types[1], &arg_values[1]);
    return TRACE_EVENT_API_ADD_TRACE_EVENT(
        phase, category_enabled, name, id,
        num_args, arg_names, arg_types, arg_values,
        kNoThreshholdBeginId, kNoThresholdValue, flags);
  }
  
  // Used by TRACE_EVENTx macro. Do not use directly.
  class BASE_EXPORT TraceEndOnScopeClose {
   public:
    // Note: members of data_ intentionally left uninitialized. See Initialize.
    TraceEndOnScopeClose() : p_data_(NULL) {}
    ~TraceEndOnScopeClose() {
      if (p_data_)
        AddEventIfEnabled();
    }
  
    void Initialize(const unsigned char* category_enabled,
                    const char* name);
  
   private:
    // Add the end event if the category is still enabled.
    void AddEventIfEnabled();
  
    // This Data struct workaround is to avoid initializing all the members
    // in Data during construction of this object, since this object is always
    // constructed, even when tracing is disabled. If the members of Data were
    // members of this class instead, compiler warnings occur about potential
    // uninitialized accesses.
    struct Data {
      const unsigned char* category_enabled;
      const char* name;
    };
    Data* p_data_;
    Data data_;
  };
  
  // Used by TRACE_EVENTx macro. Do not use directly.
  class BASE_EXPORT TraceEndOnScopeCloseThreshold {
   public:
    // Note: members of data_ intentionally left uninitialized. See Initialize.
    TraceEndOnScopeCloseThreshold() : p_data_(NULL) {}
    ~TraceEndOnScopeCloseThreshold() {
      if (p_data_)
        AddEventIfEnabled();
    }
  
    // Called by macros only when tracing is enabled at the point when the begin
    // event is added.
    void Initialize(const unsigned char* category_enabled,
                    const char* name,
                    int threshold_begin_id,
                    long long threshold);
  
   private:
    // Add the end event if the category is still enabled.
    void AddEventIfEnabled();
  
    // This Data struct workaround is to avoid initializing all the members
    // in Data during construction of this object, since this object is always
    // constructed, even when tracing is disabled. If the members of Data were
    // members of this class instead, compiler warnings occur about potential
    // uninitialized accesses.
    struct Data {
      long long threshold;
      const unsigned char* category_enabled;
      const char* name;
      int threshold_begin_id;
    };
    Data* p_data_;
    Data data_;
  };
  
  }  // namespace trace_event_internal
  
  #endif  // BASE_DEBUG_TRACE_EVENT_H_
  